The first Microbe of the Month is Helicobacter pylori, my favorite bacterium during my graduate school years.
Discovery of Helicobacter pylori
Stomach ulcers were traditionally thought to be caused by stress. However, in 1982 Barry Marshall and Robin Warren discovered that the bacterium Helicobacter pylori (H. pylori for short) is actually the cause of these ulcers. These scientists found that almost all stomach biopsies from patients with gastric ulcers also contained this helical shaped bacteria (hence the name Helicobacter). Barry and Marshall’s discovery was met with much skepticism at the time. Desperate to prove that H. pylori was indeed the cause of gastric ulcers, Marshall drank a culture of H. pylori and developed gastric ulcers that were accompanied by H. pylori in his gastric biopsies. He then cured himself of the infection by taking antibiotics. For this discovery Marshall and Warren were awarded the Novel Prize in Physiology or Medicine in 2005.
H. pylori hates stomach acid!
Despite inhabiting the stomach, H. pylori actually does not like stomach acid. H. pylori produces copious amounts of urease, an enzyme that buffers the pH around the bacterial cell. Thus H. pylori survives in the stomach because it surrounds itself with a cloud of neutral pH. However, this is not a long term solution for the survival. The bacterium must swim to the stomach mucosa lining where the pH is closer to neutral. To do so, H. pylori uses flagella, tail-like structures used to propel the organism forward. Once crossing the mucosal lining H. pylori is capable of causing disease symptoms.
http://www.nsf.gov/news/mmg/mmg_disp.jsp?med_id=66334&from=search_list
Most H. pylori infections do not cause symptoms
H. pylori is a bacterium that resides only in the stomach and the upper intestinal tract. Not only does it cause ulcers, it can also cause stomach cancer, B cell MALT lymphoma and gastritis. Interestingly, individuals who carry H. pylori in their digestive tract mostly do not show symptoms. 10-20% of infected individuals will develop ulcers in their lifetime and 1-2% of infected individuals will develop gastric cancer or B cell MALT lymphoma in their lifetime. Even more bizarre, half of the world’s population carry this bacterium in their stomach and do not show any symptoms.
H. pylori as part of the microbiome?
Since the discovery of H. pylori, it has been traditionally considered as a pathogen, but more recently, its role in human health has become more nuanced. Helicobacter species inhabit the gastrointestinal tract of many mammals and birds, and most Helicobacter species are host specific, implying a co-evolution of the bacterium with its host. In fact, H. pylori has co-evolved with humans for the past 60,000 years! Martin Blaser, a professor at New York University School of Medicine and director of the NYU Human Microbiome Project, has suggested that H. pylori may be part of the human microbiota and the decline of H. pylori colonizations in some geographical areas correspond to an increase in esophageal adenocarcinoma cases. Other studies have also linked H. pylori to both positively and negatively to a variety of diseases. However, it is currently unclear whether the trends between H. pylori and specific diseases indicate a causal relationship between H. pylori and the disease.
Please stay tuned for the next post on urban microbiomes.
